Numerous investigations have reported both positive and negative efficacy of dietary selenium in preventing or causing a variety of human conditions. Selenium is known to be an essential micronutrient for human beings; as an agent for antioxidant defense it acts as a catalyst for production of thyroid hormone and is vital for proper functioning of the human immune system. In addition, recent studies have shown that its deficiency can lead to a variety of health risks. For example, selenium deficiency is associated with increased cancer risk, occurrence of cardiovascular diseases, adverse mood states and infertility in males. In contrast, higher concentrations of selenium in human beings can be toxic. Therefore, the United States recommended dietary allowance of selenium is 55-70 ug/day for an average healthy individual.
To effectively monitor the concentrations of naturally occurring trace elements in agricultural products in the food chain, operators must be able to rapidly and efficiently perform highly sensitive analysis of trace elements in a variety of organic materials. Several laboratories have developed analytical methods to more precisely determine the amounts of trace elements present in agricultural biomass. By being able to rapidly distinguish between selenium-enriched and selenium-deficient agricultural raw materials, the operators can effectively facilitate the segregation of selenium-enriched biomass at shipping termination. For example, when a truck or train load of agricultural product arrives at the mill, the mill operators will have to decide within an hour whether the contents of the load should be assigned as a selenium-enriched raw material for premium pricing and sale. The only alternative presently available is a portable X-ray fluorescence spectroscopy method. However, this device does not provide sufficient accuracy with a detection limit and accuracy of around 10 parts per million weight. Furthermore, a major limitation of this method is that it measures only the selenium concentration in the surface layer of the material rather than its concentration in the entire sample.
In contrast, laboratory methods have higher sensitivity and accuracy but require significant processing time. These methods include spectroscopic methods such as hydride atomic absorption spectroscopy (HAAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and graphite furnace absorption spectroscopy (GFAA). Other time consuming methods include inductively coupled plasma/mass spectroscopy and neutron activation. The major bottleneck with these analytical methods is the lengthy chemical digestion step that is needed to break down plant fibers and release selenium into a liquid or gaseous phase, where it can be easily analyzed. Digestion methods typically use concentrated nitric or perchloric acids as well as hydrogen peroxide, often with heating to high temperatures. These digestions often take several hours so that the turnaround time for a single analysis is insufficient for the current application. Furthermore, much of the digestion process is manual in nature, requiring highly skilled, trained analytical technologists. It would be highly desirable to develop a method and apparatus that has the combination of speed and accuracy necessary to perform this analysis at key segregation points in the food chain with a reduced requirement for technical skills.